DESCRIPTION (adapted from the Abstract): The goal of this project is to understand the effects of mutations on the catalysis and inhibition of the HIV protease. A large number of potent inhibitors against HIV protease have now been synthesized and tested by many laboratories. A few of these are currently in clinical trials. However, increasingly, recent evidence supports the view that HIV acquires resistance to protease inhibitors by mutation of its protease. The ability to modulate separately the proteolytic activity and the inhibition sensitivity by mutation is the basis of resistance. Thus, the researchers in the current project seek basic knowledge of how mutations of HIV protease render changes in catalysis and inhibition how these changes are translated into resistance. Their project has two components: (1) to understand how the activity and inhibition are changed due to mutations of HIV protease; and (2) to determine the crystal structures of mutant HIV protease- inhibitor complexes. Mutant enzymes with characteristics of "inhibition resistance" are those which retain catalytic efficiency comparable to the wild-type enzyme but are significantly less sensitive to inhibitors. In previous studies, these researchers have observed these characteristics in several mutants. As Component #1 of this project, the Principal Investigator proposes an extensive study of potential resistant mutation sites, multiple mutations, and "neighboring" mutations. The many analytic tool will be enzyme and inhibition kinetics and a kinetic model which can predict the processing activities of mutant enzymes in the presence of inhibitors. Kinetic tools for predicting the relative vulnerability of inhibitors to resistance will be tested further. Recognizing that structural information is essential for interpreting the relationship between the structural changes by mutations and resistant kinetic behavior, the Investigator proposes as Component #2 of this project the crystallization of the most interesting mutant protease-inhibitor pairs and the determination of the crystal structures by X-ray crystallography. The new structures for the resistant mutant enzymes will be compared carefully to the structures of wild-type enzyme and non-resistant mutant enzymes. These comparison will provide insights for the kinetic data generation in Component #1.